Spring probes are commonly used for probing bare and loaded printed wiring boards for test purposes. Typically, the spring probes are inserted into a tubular receptacle or connector for ease of insertion and removal. The receptacle, in turn, is inserted into a probe plate of a test fixture. The test fixture is typically actuated by vacuum for drawing the probe plate (with the receptacles and spring probes) and printed wiring board together until the spring probes and printed wiring board are in electrical contact.
An example, of such a test fixture with spring probes mounted in tubular receptacles in a probe plate, is disclosed in U.S. Pat. No. 4,322,682.
With the advent of more concentrated circuitry and more closely spaced test points, a need has arisen for placing the probes closer together and, therefore miniaturizing the spring probes and receptacles. At the current time a need exists for low cost, easy to assemble miniature spring probes and receptacle assemblies of about 0.036 inches (0.914 millimeters) or smaller in overall diameter, which can be mounted for probing test points spaced 0.050 inches (1.27 millimeters) on center or closer.
The receptacles are each terminated to an insulated flexible wire. Several different techniques exist for termination. For example, insulated wires are crimped or soldered to receptacles.
However, it is generally desirable to use replaceable or reusable terminations. One such prior art device has a stripped insulated wire passed through the center of and bent around the side of a nylon plug which, in turn, is inserted in the end of a tubular receptacle wedging the wire between plug and receptacle.
A further prior art device has a stripped insulated wire inserted in the end of and soldered to a tubular shaped wire plug. The plug is inserted into the end of the tubular receptacle for a spring probe. An insulated sleeve is mounted around the end of the plug and onto the insulated wire so as to prevent electrical contact between the adjacent ends of crossed closely spaced receptacles and for strain relief for the wire.
Another prior art device employs a gold plated brass machined wire plug with pinchers. The wire plug with pinchers is machined into a tube with stepped outer diameters and a pair of pinchers is machined extending from one end of the tube. A short insulator sleeve is mounted around the plug adjacent the end opposite to the pinchers. Insulated wire is stripped to provide a bare end, which is passed through the center of the tube and between the pinchers. The wire plug with the wire is inserted into the end of a tubular spring probe receptacle, which has a restriction or squeeze point which, in turn, squeezes the pair of pinchers together against the wire, gripping and holding the wire in electrical and mechanical engagement with the plug.
The prior art approaches using plugs pose difficulties. It is difficult, for example, to make the miniature plug and mating receptacle because of the small size of the receptacle which must be in the order of 0.036 inches outer diameter or smaller. Additionally, there are undesirable expenses and time consumed in machining the wire plug with pinchers. Also, the insulator sleeve on the wire plug with pinchers is very short and may not adequately insulate adjacent receptacles, should they become bent and crossed which is not unusual because of the small fragile nature of the small diameter miniature receptacle.
Further with receptacles closely spaced (i.e., 0.05 inch on center) there is virtually no room on the sides of the receptacles or, because of adjacent wiring, even close to the ends of the receptacles for one to put a tool or fingers to assist in making up a wire to the receptacle. This makes it quite difficult to insert the short plug used in the wire plug with pinchers device.